Testing accuracy of lens shutter speeds

Darwinean_JohnUK

Darwinean_JohnUK

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Whilst I very often I use the tiny format (35mm) and medium format lenses in Av exposure mode, I do also use fully manual mode. On all large format, and occasionally on the smaller formats, I also manual exposure.
I need to check the accuracy of shutter speeds on all lenses I use for manual exposure. I have found a few suggestions on-line for electronic circuits and software that can be used to do these measurements but haven't got any to work. Have you had any of your lenses tested and maybe even been fully or partially rectified? If so, who did it?
 
Check a really long exposure as accurately as you can with a stopwatch, say 20 sec, take the average of maybe a dozen shots. Once that's established as a base reference you can check all the others against it by checking the exposure as you increase shutter speeds and increase ISO or aperture.

I'm puzzled by your suggestion that shutter speed accuracy is associated with lens. Note that different lenses will pass different amounts of light at the same aperture which on auto exposure would cause a different shutter speed to be selected, nothing to do with accuracy of shutter speeds.

You can calibrate all your apertures against one for each lens in the same way. Calibrating all shutter speeds or apertures against one means that one precise measurement in absolute terms will recalibrate the lot.

You say you need these results for manual exposure. But almost all cameras with an auto exposure function allow you to see by how much your manual exposure diverges from what the auto exposure system measures. Use of manual aperture rings or of preview button to stop down will remove lens aperture idiosyncrasies from the auto exposure measurements. I think you should describe the problem you're trying to solve in more detail.
 
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Current digi guys used to use film and have a lot knowledge on these matters. Film guys come in this section too. Some are both digi and film. This section is about equipment not just digi equipment
 
I have a shutter speed tester which I built. Basically an oscillator driving a counter which is gated by a photo-transistor looking at a light through the lens. I think the oscillator runs at 10kHz so a 1 millisecond or 1/1000 second speed is a count of ten.

If you have an oscilloscope, you can just look at the opening time on screen using a light and a photo-transistor (with a voltage source and pull up resistor).


Steve.
 
Cheers Steve, I haven't got an oscilloscope but some sware on Mac that appears to do the same. My attempts at circuit building appears to be the weak link. But your circuit description appears to be the simplest I've seen (eg no capacitor needed). Can you give me an indication of the size of each component? I'm designing and testing on bread board before making a permi circuit.
 
Darwinean_JohnUK said:
Current digi guys used to use film and have a lot knowledge on these matters. Film guys come in this section too. Some are both digi and film. This section is about equipment not just digi equipment
Click to expand...

It was just a suggestion to get some more visibility from other LF shooters that may not venture outside of the F&C section but no problem.
 
Leaf shutters take time to open and close. This time factor is even greater on large format lenses because of the physical dimensions.
Leaf shutters also vary in their exposure according to the aperture used at a particular shutter speed.
at a large aperature the light is progressively let in as the shutter blades open and reduces as they start to close.
on small apertures most of the opening and closing time is masked behind the aperture blades.
If they are electronically controlled the time spent fully open should be fairly accurate. Fully mechanical shutters are rarely accurate. But if they are well serviced they should be repeatable.

What is more important with a leaf shutter is that you know the relative exposure each shutter seed gives..rather than its actual speed.

In real life few photographers have ever done this. As life is too short, and the results are both depressing and rarely truely useful.
Even on a shutter in pristine condition the higher speeds only have a token resemblance to that marked,
 
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